Question About Photoshop and Lightroom Memory

I do photography and use Lightroom and Photoshop on my 13" Macbook Pro (hooked up to a cinema display) with 4GB RAM and a NVIDIA GeForce 9400M graphics card with 256MB.

When I apply filters or some actions Photoshop seems to crawl. Of course this when I also have Lightroom running.

Do you think this is because of the graphics card or RAM memory limits? I have been thinking of upgrading from 4GB to 8Gb, but that runs $450.00. So I really dont want to spend that money to find out that its really the graphics card is the real problem.

MacRumors attracts a broad audience
of both consumers and professionals interested in
the latest technologies and products. We also boast an active community focused on
purchasing decisions and technical aspects of the iPhone, iPod, iPad, and Mac platforms.